This invention relates to a T-root, centrifugal turbine rotor blade manufactured from sheet stock and to a method for its manufacture.
The manufacture of centrifugal turbine rotor blades in sheet construction has long been attempted. These blades have not matured for series production, however, at least not for use on high-speed rotors, because it was impossible to safely attach them on the hub. The connection of the blade to the hub requires a high-strength material and, moreover, optimum transfer of forces, i.e., a design minimizing stress concentrations. This could not be achieved, however, with the conventional welding and brazing methods. The practice was, e.g., to join blades to the hub by their unmodified front edge, when welding caused unacceptable undercutting and/or notching in the weld transition. The practice of bending the end of the blade into L-shape and of joining the L-leg, which extended in parallel with the hub, to the hub occasioned, under high centrifugal loads, bending moments which in turn caused the brazed or welded joint to separate. The same was bound to happen when the bent L-end of the blade was additionally fitted with a sheet angle to form a T-root. The inevitable outer radii of the L-bends again produced bending moments and separating loads on the joint.
In a broad aspect, the present invention provides a centrifugal blade made from sheet stock for safe connection to the rotor hub also under extremely high loads.
It is a particular object of the present invention to provide a centrifugal blade of the above generic category where the T-root of the blade is formed by shaping the rim of the sheet stock under pressure.
This gives a flat blade root suitable for joining to the rotor hub by brazing, welding or also explosive welding in that it offers a wide cross-section for connection without stress raisers.
Another object of the present invention is to provide a centrifugal blade for the foregoing character which may be economically fabricated and which has a substantially long operating life.